1. Field of the Invention
The present invention relates to an image scanner and, more particularly, to an image scanner for reading images by radiating light onto a given original document and by reading with CCD sensors the light reflected therefrom.
2. Description of the Related Art
Hitherto, image reading means called image scanners for radiating light onto an original document from a light source, reading light reflected from this original document by means of a plurality of arrayed CCD sensors, converting the image information of the original document into electrical signals and outputting the signals have been used in peripheral units of a computer and recording apparatuses having image reading means incorporated therein.
A conventional image scanner will be described below. FIG. 3 shows a conventional image scanner. An image scanner 31 has a box-type unit case 32 in the shape of a rectangle, with an opening 33 substantially in the shape of a square being formed in such a manner as to face a given original document (not shown) at one end surface of the unit case 32 along the length thereof. This opening 33 has a length dimension which extends substantially across both sides of the unit case 32.
Further, holding plates 34 which are extendedly provided along the side surface of the unit case 32 are integrally formed in both side portions of the inside of the opening 33 of the unit case 32 in such a manner as to project inwards, and the inner edge of the holding plate 34 has an inner wall 34a formed so as to extend in the direction of the opening 33.
A recess-shaped lamp housing section which is opened toward the opening 33 is formed between the inner wall 34a of the holding plate 34 and the inner side surface of the unit case 32, and a circular-cylinder-shaped lamp 35 is disposed in the innermost portion of the lamp housing section. Further, a light-source lens 36 is disposed in the opening portion of the lamp housing section.
Further, in the side surface portion of the inside of the unit case 32 of the holding plate 34, a slit which extends along the side surface of the unit case 32 is formed and a substrate 37 having a conductor pattern for supplying power to the lamp 35 is disposed.
FIG. 4 shows the substrate 37 and the conductor pattern 38 thereof. The substrate 37 is formed substantially in the shape of a .quadrature. symbol in its plane shape by glass epoxy which is a light transmitting material, and the conductor pattern 38 is formed only in a portion required for wiring on the surface of the inside of the unit case 32 of the substrate 37.
A further description will now be given. The conductor pattern 38 is formed of a conductor pattern 38a for connecting either the positive or negative terminal of the lamp 35 and a conductor pattern 38b for connecting the other terminal. The conductor patterns 38a and 38b are formed only in a part of the inner surface of the unit case 32 of the substrate 37, and the substrate 37 made of a light transmitting material is exposed at the portion where the conductor pattern 38 is not formed so as to provide electrical insulation. Further, a terminal 39 connected to both sides of the lamp 35 is extended from the slit into the interior of the unit case 32, so that the terminal 39 is electrically connected to the conductor pattern 38 formed on the substrate 37.
By turning on the lamp 35 by supplying electric current thereto, radiation light from the lamp 35 is radiated from the opening of the unit case 32 via the light-source lens 36 to the outside so that a desired original document (not shown) placed near the opening 33 is radiated.
Further, a CCD sensor 40 is disposed at the end portion of the inside of the unit case 32 on the side opposite to the opening 33, and a circular-cylinder-shaped lens unit 41 is disposed between the opening 33 and the CCD sensor 40 in the inside of the unit case 32. The lens unit 41 includes a light entry section 42 for admitting light which is radiated from the lamp 35 via the light-source lens 36 and which is reflected from the original document, and a light emergence section 43 for causing this light to exit to the CCD sensor 40, with a plurality of image forming lenses 44 and 44 for focusing the incident light from the light entry section 42 so as to form an image on the CCD sensor 40 being disposed with a predetermined space therebetween in the inside of the lens unit 41.
In the above-described conventional image scanner 31, an intended original document is first placed near the opening 33 of the image scanner 31, and the image scanner 31 and the original document are moved relative to each other in a state in which the lamp 35 is switched on. As a result, the radiation light from the lamp 35 is radiated from the opening 33 through the light-source lens 36 onto the original document, after which the light is reflected by this original document, is made to re-enter the unit case 32 from the opening 33, and enters the light entry section 42 of the lens unit 41 after passing through the space between the holding plates 34.
The light entering the lens unit 41 is collected by the image forming lenses 44 of the lens unit 41 and is radiated onto the CCD sensor 40 from the light emergence section 43. Thus, image information from the original document is obtained by the CCD sensor 40.
However, in the above-described conventional image scanner 31, since the opening 33 has a length dimension which extends substantially across both sides of the unit case 32, the light from the light-source lamp 35 is radiated over a wide range of the original document. For this reason, a large amount of light is reflected from portions out of the actual reading range of the original document, and this unwanted reflected light is collected by the lens unit 41 and received by the CCD sensor 40. As a result, there is a problem that the contrast of the image of the original document decreases, resulting in a considerable decrease in reading accuracy.
There is another problem in the image scanner 31 in that light radiated from the lamp 35 is randomly reflected by the light-source lens 36, such radiation light is radiated not only onto the original document surface, but also onto the inside of the unit case 32 and directly radiated onto the lens unit 41, resulting in a decrease in the contrast of the image of the original document and a decrease in reading accuracy.
There is a further problem in the image scanner 31 in that light radiated from the lamp 35 leaks from the slits formed in the holding plates 34 and 34 and from the portion of the substrate 37 made of a light transmitting material where the conductor pattern 38 is not formed, and this leaked light is directly radiated onto the lens unit, resulting in a decrease in the contrast of the image of the original document and a decrease in reading accuracy.
Even with an image scanner having the above-described problems, in a case in which the image of the original document to be read is a monochrome image and read by binarization, a major problem is not incurred even if the contrast of the image is poor. However, in a case in which the image of the original document is in color and is read at multi-valued gradations of, for example, 256 in order to obtain color image information, unwanted light such as that described above is input and the contrast of the image is decreased, and a problem occurs in which the quality of the image to be read decreases.
If a non-light-transmitting material is used for the above-described substrate, at least the problem of light leaking from the substrate is overcome; however, use of materials other than inexpensive glass epoxy results in a high price. Further, if coloring is performed to make the substrate made of a glass epoxy material non-permeable to light, a problem occurs in that the number of steps therefor increases, resulting in increased cost.